Princess Diana Memorial Playground

Playground as a Memorial to Diana Princess of Wales, Kensington Gardens, London

The playground is based on Sir JM Barrie’s 1904 play “Peter Pan”, incorporating a Pirate Ship, crocodile, fountains, and wig-wams, as well as the more standard playground equipment. The “home underground” plays a part in the original story, and it was this theme that was used for the new building containing the children’s lavatory and attendant’s offices. The Architectural form comprised a buried building, with organically curved roof and walls. The task was to develop a structural form that could be economically built within the tight budget and programme.

The final solution, as built, comprises an in-situ concrete shell structure, 150 millimetres thick, sprayed from the inside onto a reinforcement mat covered with thin reusable polycarbonate sheets as formwork. The concrete shell is then finished with an internal plaster surface, and with waterproofing provided by a combination of external tanking on the sprayed concrete areas and a hydrophobic additive in the ground floor slabs and walls.

The most difficult problem to resolve was the construction of the concrete shell without an expensive rigid formwork system. Since the construction of the Sydney Opera House, the useful geometrical properties of a torus have been well known. Barton Engineers have used these concepts on a number of projects. In this instance the shell surface geometry was set down as being a part of a torus, or doughnut shape, so enabling a three dimensional curved surface to be created using a series of constant radius curved elements.

A primary grid shell of 20 mm diameter reinforcing bars was erected first; each bar length was computer generated with all bars having the same radius. This primary grid took two days to create. When 6 adjustable props had been placed under specified key nodes, it was stiff enough to support the shell reinforcement proper, which comprised 8 mm diameter straight bars at 150 mm centres in each direction and in two layers. Finally layers of thin flexible polycarbonate formwork were laid over the whole surface, and the shell concrete sprayed in layers from the inside. The whole process took less than two weeks and resulted in a concrete shell built to relatively high tolerances, and with no rigid formwork or falsework.